The present invention relates to an improved apparatus for deslagging tubes in a steam generator by the application of high frequency shock energy.
It is well known that in the operation of a steam generator slag builds up on the tubes or heat transfer surfaces from the soot and ash which accumulate thereon. This slag causes a great loss of heat and seriously impairs the efficiency of the steam generator unless it is removed frequently and thoroughly. Slag which has built up on roof tubes of a steam generator also poses a safety menace because it may fall on maintenance personnel working inside of the steam generator furnace. Numerous devices and methods have been proposed to clean or deslag such tubes but all have certain limitations and disadvantages and none are wholly satisfactory.
Removing slag from steam generator tubes has also become more difficult and expensive as steam generators have increased in size and replacement power costs have increased. With certain steam generator designs, for example, there is limited access to problem areas because of fewer access doors. With a wide furnace, the doors may be too far apart to attack the accumulated slag manually. Increased steam generator height also means that the falling slag's destructive force is multiplied due to its increased terminal velocity. For example, a 100-lb slag fragment has an impact force of 14,000 ft/lbs based on a 150-ft fall versus 9,938 ft/lbs for a 100-ft fall. Obviously, a hard hat offers little or no protection from this large a threat.
Several techniques for removing the slag from the tubes of such large steam generators have been tried by maintenance personnel but found unsuccessul. These include water sprays which provide some thermal shock and impact, but generally not enough to provide significant removal; shotgun blasts which have insufficient impact to dislodge slag; soot blowers which cause tube erosion, adding to the problem; and air hammers applied at random to the tubes which are potentially damaging to the tubes and the operation of which is hot and dusty work requiring very short worker shifts to prevent heat exhaustion.
There have also been numerous arrangements proposed for vibration cleaning of heat exchange tubes. For example, Russian Pat. Nos. 309,223 and 454,413 disclose arrangements wherein horizontal coil tubes in a gas duct are fixed on support beams which in turn are connected to vibrators. The support beams are able to move in the gas duct and transmit vibration from the vibrators to the tubes. However, this type of arrangement may not be practical for large steam generators where sealing problems become difficult because of the high pressures therein during operation and where the size of support beams is too great because of the steam generator size. Further, the tubes are generally not suspended for movement in such large steam generators but are secured to stationary components of the steam generator as in the case of the roof tubes in a large steam generator which are securely connected to stationary support beams. In these large steam generators temperatures as high as 4000.degree. F. may also require the use of exotic metal beams or cooling.
Another vibration cleaning technique is that proposed in U.S. Pat. No. 4,018,267 where the tubes are suspended for movement within the heat exchanger and are oscillated with an amplitude of vibration such that the tubes impact against each other to jar the slag or dust accumulations therefrom. Special suspension arrangements are necessary to mount the tubes so that they may move in this manner. Therefore, this technique is not suitable for large radiant type steam generators wherein the tubes are normally securely fixed in position. The shock on impact of the tubes may also cause stress problems at the elevated temperature found in modern steam generation. Morover, this known technique may be problematical because of the seals which are required about the moving parts. These seals must withstand high pressures in the case of large steam generators as noted above.
It has also been disclosed that for off-line vibration cleaning of roof tubes in a steam generator, the impact from a pneumatic vibrator may be transmitted to the roof tubes by way of a buckstay or wide flange beam of the steam generator which carries the roof tubes. This technique has been found lacking, however, because a significant percentage of accumulated slag cannot be removed from the tubes during cleaning. One possible explanation for this is the inefficient transfer of the high frequency shock energy from the vibrators to the tubes via the buckstays. Such an arrangement is also impractical for use with other tubes of the steam generator such as nose end tubes, superheater tubes and sidewall tubes which are not supported from the buckstays or wide flange beams of the steam generator in a manner permitting the transmission of impact from the vibrators to the tubes.
Thus, an object of the present invention is to provide an improved apparatus for deslagging tubes in a steam generator which avoids the aforementioned disadvantages associated with the known techniques. More particularly, an object of the present invention is to provide an apparatus for deslagging tubes in a steam generator by the application of high frequency shock energy whereby high frequency shock energy is efficiently transmitted from a vibrator which may be located outside of the steam generator to tubes located in the steam generator.
An additional object of the invention is to provide an apparatus for deslagging tubes in a steam generator by the application of high frequency shock energy wherein the tubes of the steam generator need not be suspended for large amplitude oscillatory movement but may be securely fixed in position to a support beam or other structure at various locations within the steam generator.
These and other objects of the invention are attained by providing an apparatus comprising vibrator means for producing high frequency shock energy, base plate means for distributing the high frequency shock energy over a relatively large area encompassing portions of a plurality of steam generator tubes, and means connecting the vibrator means to the base plate means for transmitting high frequency shock energy from the vibrator to the base plate means, the connecting means including at least one interference fit tapered connection, and wherein means are provided for securing the base plate means in a position adjacent the plurality of tubes while allowing for thermal expansion of the tubes during operation.
According to one disclosed embodiment of the invention, the tubes to be deslagged are roof tubes of a steam generator which are supported at a plurality of spaced locations along their length from beams of the steam generator. In this embodiment, the base plate means of the apparatus is located against the upper surface of the roof tubes at a position spaced from the beams supporting the tubes. The roof tubes are defined by a roof tube membrane of the steam generator. The means securing the base plate means in position adjacent the roof tubes includes clips which are secured to the tube membrane and extend along side of and over the base plate means thereby retaining the base plate means in position against the tubes to effect good transmission of energy while allowing for thermal expansion of the tubes during operation of the steam generator. The vibrator means is a pneumatic vibrator which is located above a penthouse roof of the steam generator in the disclosed arrangement. The connecting means of the apparatus includes shaft means which extends from the vibrator down into the steam generator to the base plate means for transmitting high frequency shock energy from the vibrator to the base plate means. The shaft means is connected at its ends to the vibrator and the base plate means by respective interference fit tapered connections.
In another application of the invention, the tubes to be deslagged are parallel nose tubes of the steam generator, a portion of the nose tubes extending inwardly and upwardly from a sidewall of the steam generator. The base plate means of the apparatus of the invention contacts the inwardly and upwardly extending portions of the tubes. The means securing the base plate means in position adjacent the tubes includes clips which are secured to the tubes about the base plate means and which extend along side of and over the base plate means thereby retaining the base plate means in position against the tubes while allowing for thermal expansion of the tubes during operation of the steam generator. The parallel nose tubes of the steam generator are supported in part by hanger rods which are connected to the inwardly and upwardly extending portions of the tubes. The base plate means of the apparatus is located against the upper surface of the inwardly and upwardly extending portions of the tubes at a position spaced from these hanger rods. The connecting means of the apparatus includes a shaft means connected at one end to the vibrator means by an interference fit tapered connection for transmission of high frequency shock energy from the vibrator means to the shaft means, with the base plate means being connected to the other end of the shaft means by an interference fit tapered connection for transmission of high frequency shock energy from the shaft means to the base plate means. The shaft means extends obliquely with respect to the plane of the nose tubes at the base plate means and toward a side wall of the steam generator.
In another embodiment of the invention, the tubes for deslagging are side wall tubes of a steam generator which are defined by a tube membrane. In this application, the means securing the base plate means in position adjacent the tubes includes a plurality of fasteners which are connected to the tubes and which extend with clearance through openings in the base plate means to allow for thermal expansion of the tubes during operation. Means are provided on the fasteners for resiliently biasing the base plate means against the tubes. The connecting means of the apparatus includes a pin plate which is located intermediate the base plate means and the means for resiliently biasing the base plate means. The pin plate is connected to the vibrator means by at least one interference fit tapered connection. In the disclosed arrangement, the fasteners are connected to the tube membrane by welds.
In another embodiment of the invention, the tubes to be deslagged are two rows of spaced parallel essentially vertically extending superheater tubes of the steam generator. The vibrator means of the apparatus is located between the two rows of tubes and is coupled by the connecting means to two base plate means contacting the respective rows of superheater tubes. Each of the two base plate means extends in a direction at right angles to the longitudinal direction of the superheater tubes. The means securing the two base plate means in a position adjacent the tubes includes a contoured surface on each of the base plate means which receive the plurality of superheater tubes and tangentially surround portions thereof to prevent lateral shifting of the base plate means with respect to the tubes while allowing for the thermal expansion of the tubes, especially in the longitudinal direction, during operation.
In each of the disclosed embodiments of the invention, the apparatus preferably includes a plurality of vibrator means for producing high frequency shock energy. The vibrators are located at a plurality of spaced locations spaced from the tubes of the steam generator to be deslagged. A plurality of base plate means for distributing the high frequency shock energy over a relatively large area encompassing portions of a plurality of the tubes are provided. Each of the base plate means is located against the surface of the tubes at a position spaced from the support means for the tubes. A plurality of connecting means connect the vibrators to the respective base plate means for transmitting high frequency shock energy from the vibrators to the base plate means. Each of the connecting means includes at least one interference fit tapered connection. Means are provided for securing the base plate means in position adjacent the tubes while allowing for thermal expansion of the tubes during operation of the steam generator.
The disclosed embodiments illustrate the application of the invention for deslagging roof tubes, nose tubes, side wall tubes and superheater tubes of a steam generator. The invention may also be used to deslag tubes in other areas of the steam generator, such as the throat. Thus, by means of the invention it is possible to efficiently deslag the various tubes of a large steam generator. Moreover, since special suspensions for the boiler tubes need not be employed, the apparatus of the invention can be readily adapted to existing steam generators to improve operating efficiency and reduce the risks of injury to maintenance personnel. The invention is also useful for deslagging tubes of operating, as well as off-line steam generators.
These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the invention.